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VERTEBRATES > DINOSAURS > Flashcards

DINOSAURS Flashcards

1
Q

What group did dinosaurs evolve from?

A

The Archosauria
(a monophylectic group)

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2
Q

What are the synapomorphies of archosaurs?

A
  • Presence of calcaneal tuber - bone projecting from ankle - flexor muscle is attached
  • 2 skull opening - one in lower jaw, hypothesised that it was where jaw muscles attached.
  • Second skull opening is between eye socket and nostrils - hypothesised: adaptation for reducing skull weight
  • Presence of teeth in sockets - roots that are not fused to the jaw. Thecodont.
  • Reduction in the 5th toe
  • Secondary palate (allow them to breath whilst eating)
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3
Q

What are the 2 major clades within archosauria?

A
  1. Pseudosuchia
  2. Ornithodira
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4
Q

What were the Pseudosuchia?

A
  • Reptiles & crocodilians
  • High diversity during mid - late triassic
  • Only extant group crocodiles
  • Quadrupeds and some facultative bipeds
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5
Q

What were the Ornithodira?

A
  • Pterosaurs, dinosaurs + primitive relatives
  • Non-avian dinosaurs and birds
  • Simple hinge-joint ankle
  • Very long hindlimbs
  • Longer s-shaped neck
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6
Q

Which was more prominant, Pseudosuchians or dinosaurs when dinos first appeared?

A
  • Pseudosuchians
  • Ruled by reptiles
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7
Q

What were the shared derived features of dinosaurs?

A
  • The semi-erect posture (more upright)
  • Limbs positioned directed below the shoulders
  • Pubis bone - downwards and backwards
  • Hip joint
  • S-shaped neck
  • Reduction in 4th and 5th digit on hand
  • Reduction to 3 main toes on foot
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8
Q

What are the characteristics of the dinosauria hip?

A
  • Open acetabulum (hip socket)
  • Sacrum - fused vertebrae
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9
Q

What are the two major clades within dinosauria?

A
  1. Ornithischians
  2. Saurischians
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10
Q

What is the clade saurischians comprised of ?

A
  • Sauropodomorphs
  • Theropods (including birds)
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11
Q

How did two groups evolve based on the study of the hip joint ?

A
  • Difference is in the pubis bone
  • In Ornithischian the pubis is aligned and parallel with the ischium - facing backwards by tail
  • In Saurischians pubis points forward and flares into keel
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12
Q

How is the hip positioned in the Ornithischians?

A

pubis is aligned and parallel with the ischium - facing backwards by tail

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13
Q

How is the hip positioned in the Saurischians?

A

pubis points forward and flares into keel

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14
Q

Which group are ‘Lizard Hip Dinosaurs’?

A

Saurichians

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15
Q

Which group have ‘Bird Hips’?

A

Ornithischians

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16
Q

Which hip dinosaur group did modern birds evolve from?

A

Lizard Hip Dinosaurs
Bird hipped dinosaurs did not include birds

17
Q

How has dinosaur phylogeny been reworked?

A
  • Evolutionary tree was shuffled about and a new phylogeny hypothesis was established including new clade Ornithocelidans. WIP
  • This would mean birds evolved from bird-hip dinosaurs
18
Q

Features of reproduction in dinosauria

A
  • Study extant dinosaurs and infer behaviour of dinosaurs
  • All extinct dinosaurs laid eggs (this is known)
  • Hard-calcium carbonate shell - was widely accepted to be the only type of eggs that dinosaurs laid.
  • Did they develop from soft egg shells? Leathery (like turtle eggs)
  • Fossil bias - most are from cretaceous - were the earlier eggs soft and so unpreserved
  • Sexual dimorphism - larger females?
  • Male competition - all very hypothetical
19
Q

Diversity of dinosaurs

A
  • More is known about the extinction of the dinosaurs that how they diversified
  • 700 - 800 groups
  • Only around 5% excavated from triassic rocks
  • Birds are the only group of dinosaurs that survived from the cretaceous period
20
Q

What is the most accepted hypothesis for the extinction for non-avian dinosaurs?

A

Asteroid in the yucatan peninsula

21
Q

Were dinosaurs declining before the extinction event?

A
  • End of cretaceous was a changing time (environmental etc)
  • Study suggested that dinosaurs were declining about 10 million years before the asteroid caused extinction
22
Q

What drove the delcine in dinosaurs before the asteroid?

A
  • Abiotic factors (climate, temperature, sea level etc)
  • Biotic factors (diversity of ferns, evolution of angiosperms etc)
  • Diversity dependence (interaction between carnivores and herbivores)

Two factors were at play that explain decrease

  1. Temperature - global cooling climate
  2. Density of herbivorous dinosaurs
23
Q

Birds evloved in the triassic, diversified in the jurrasic and are the only group of dinosaurs to survive the end of the cretaceous period

A

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